1. Field of the Invention
The present invention relates generally to a visual recognition apparatus for use in, for example, a robot, and more particularly to an optical information processor used in the visual recognition apparatus for performing image processing or image recognition.
2. Description of the Prior Art
Recently, there have been strong demands in the field of image processing or image recognition for processing a large number of pixels faster than that hitherto accomplished. To this end, an optical information processor making use of a high-speed parallel operation has been developed.
Japanese Laid-open Patent Publication (unexamined) No. 2-132412 discloses an optical information processor as shown in FIG. 1. In FIG. 1, reference numeral 20 denotes a TV camera; reference numeral 21 denotes a first liquid crystal display for displaying an image picked up by the TV camera 21; reference numeral 22 denotes a laser diode; reference numeral 23 denotes a collimator lens for collimating light from the laser diode 22; and reference numeral 24 denotes a first lens. The first liquid crystal display 21 is positioned on a first focal plane of the first lens 24 adjacent the collimator lens 23. Reference numeral 25 denotes a second liquid crystal display positioned on a second focal plane of the first lens 24 opposite to the first focal plane.
Furthermore, reference numeral 26 denotes a ROM (read-only memory); reference numeral 27 denotes a second lens; and reference numeral 28 denotes a photodetector. the ROM 26 are stored data of computer-generated Fourier-transform holograms obtained as a result of a calculation performed using pixels of the second liquid crystal display as sampling points against a plurality of reference patterns. These data are indicative of data of applied voltages corresponding to the transmittance of the individual pixels of the second liquid crystal display 25. The second liquid crystal display 25 and the photodetector 28 are positioned on first and second, opposite focal planes of the second lens 27, respectively.
The above-described conventional optical information processor operates as follows.
An image of an object picked up by the TV camera 20 is initially displayed on the first liquid crystal display 21. The laser diode 22 applies to the first liquid crystal display 21 a coherent beam collimated by the collimator lens 23. Because the first liquid crystal display 21 is positioned on the first focal plane of the first lens 24 adjacent the collimator lens 23, a Fourier-transform image of the object optically transformed by the first lens 24 is formed on the second focal plane of the first lens 24 and, hence, on the second liquid crystal display 25.
When the data stored in the ROM 26 are applied to the second liquid crystal display 25, the transmittance of each of the pixels of the second liquid crystal display 25 is spatially modulated. As a result, each of the computer-generated Fourier-transform holograms of the specific reference patterns, which functions as an optical filter, is displayed on the second liquid crystal display 25.
Accordingly, on the second liquid crystal display 25, the Fourier-transform image, which has been optically transformed by the first lens 24 from the image of the object displayed on the first liquid crystal display 21, is superimposed on each of the Fourier-transform images.
Furthermore, because the second liquid crystal display 25 is positioned on the first focal plane of the second lens 27 adjacent the display 25, when the Fourier-transform image of the object coincides with that of a specific reference pattern, i.e., when both indicate the same object, a bright point appears on the second focal plane of the second lens 27 opposite to the first focal plane thereof and is subsequently detected by the photodetector 28. In this way, an optical image processing is performed wherein an optical filter, which takes the form of a computer-generated hologram and is displayed on the second liquid crystal display 25, functions as a matched filter.
The above optical information processor has, however, a problem in that the optical path is long for the following reasons, contributing to the size of the apparatus. Let the wavelength of the laser diode 22, the pixel pitch of the first liquid crystal display 21, and the diameter of a Fourier-transform image displayed on the second liquid crystal display 25 be denoted by .lambda., P, and D, respectively. In this case, the focal length f of the first lens 24 is given by f=D.multidot.P/.lambda.. When P=50 .mu.m, .lambda.=0.multidot.8 .mu.m, and D=60 mm, a lens having a focal length of 3,125 mm is required. Accordingly, as shown in FIG. 1, the distance between the first liquid crystal display 21 and the second liquid crystal display 25 results in 2.multidot.f=6,250 mm which is extremely long. In short, the pixel pitch P of a spatial light modulator such as, for example, a liquid crystal display is generally ten or more times greater than that of a photographic dry plate, and therefore, a long optical path is required. As a matter of course, the long optical path makes optical information processors large.